1. Field of the Invention
This invention relates to a supporting structure for a magnetic head.
2. Description of the Related Art
Conventionally, a cantilever-type flat supporting member has been widely used as the supporting structure for a magnetic head. FIG. 4 is a perspective view of such a conventional supporting structure, which consists of a load beam 1 in the form of a flat supporting plate, to the free end of which is attached a magnetic head 5 through the intermediation of a gimbal spring (not shown). Attached to the other end of the load beam 1 is a mounting plate 4. As shown in FIG. 4, the side edges of the load beam 1 are bent as indicated at 1c, 1c, the load beam 1 generally exhibiting an isosceles-triangle-like configuration. The side edges of that portion 1d of the load beam 1 which corresponds to the base of this isosceles triangle are not bent. That portion of the load beam 1 which is equipped with the bent side edges 1c, 1c exhibits a high rigidity, so that the elasticity of the load beam 1 is concentrated on the portion 1d having no bent side edges. Because of this construction, the bent side edges 1c, 1 c of the load beam 1 provides the requisite rigidity for allowing the load beam to follow any undulation of an associated magnetic recording medium.
Information recording apparatuses today are required to be smaller in size and higher in speed. In this context, any unnecessary vibration of the supporting structure for a magnetic head is undesirable since it will adversely affect the operation of the associated information recording apparatus. For example, such a vibration may cause the magnetic head to strike against the magnetic disc. When performing a seeking operation at high speed, in particular, a vibration from outside inevitably occurs and the head section is swung in the seeking direction, with the result that a vibration in a torsional mode is generated in the flat head supporting member. In an experiment, mechanical vibrations of various frequencies were applied to magnetic head supporting structures to examine how the amplitude of the magnetic head changes in response to these vibrations. FIG. 2 shows the results of this experiment. The solid line represents the frequency response characteristic of a conventional head supporting structure. In FIG. 2, the amplitude peaks at frequencies of around 2KHz and 3KHz indicate vibrations in a torsional mode. FIGS. 5(a) and 5(b) show how such torsional mode vibrations occur to the load beam 1. FIG. 5(a) shows a vibration mode at a frequency of around 2KHz. In this case, the entire flat portion of the load beam 1 is twisted except for the mounting plate 4. FIG. 5(b) shows a vibration mode at a frequency of around 3KHz. In this case, only that portion of the load beam 1 which corresponds to the base of the isosceles triangle is twisted. Thus, at frequencies of around 2KHz and 3KHz, the load beam 1 suffers torsion, which means the magnetic head cannot take an ideal posture at these frequencies. This frequency response characteristic of the magnetic head makes it difficult to design the associated servo system in such a way that it works properly while the magnetic disc drive device is in operation. Further, if there is a dispersion in the production of the load beam 1, the frequency of its vibration may fluctuate to an excessively large degree, resulting in a deviation from the setting of the compensation circuit in the servo system. In the worst case, the servo system may malfunction, resulting in a seeking error. The amplitude might be diminished by augmenting the thickness of the load beam. That, however, will also heighten the rigidity in the bending direction of the beam, thereby making it difficult for the head to follow the undulation of the magnetic recording medium.